Phosphorus compounds flame retardants

Phosphorus -bromine flame retardant synergy was demonstrated in a 2/1 polycarbonate/polyethylene blend. These data also show phosphorus to be about ten times more effective than bromine in this blend. Brominated phosphates, where both bromine and phosphorus are in the same molecule, were also studied. In at least one case, synergy is further enhanced when both phosphorus and bromine are in the same molecule as compared with a physical blend of a phosphorus and a bromine compound. On a weight basis, phosphorus and bromine in the same molecule are perhaps the most efficient flame retardant combination. The effect of adding an impact modifier was also shown. 

The mode of action of phosphorus-based flame retardants is believed to take place in either the condensed or the vapor phase (refs. 1,2) depending on the type of phosphorus compound and the chemical composition of the polymer. Phosphorus has been reported to be 3 to 8 times more effective than bromine depending on the polymer type (ref. 3). 

Ishizu has reported on the toxicity towards mice of these compounds and their acyclic precursors (75MI1). They appear to be somewhat less toxic than other phosphorus-containing flame retardants. 

Phosphorus-containing flame retardants are suitable for polar polymers such as PVC, but for polyolefins their action is not sufficient. In this case they are used together with Sb203 and with halogenated compounds. Alkyl-substituted aryl phosphates are incorporated into plasticized PVC and modified PPO (Noryl) to a great extent for other plastics they are less important. Quaternary phosphonium compounds are recommended as flame retardants for ABS and polyolefins. 

Inorganic phosphorus compounds are also used as flame-retardants. Elemental red phosphorus itself is applied, for example, in polyurethane foams and more recently in polyamides. Some marketed types of red phosphorus-based flame-retardants are collected in Table 5.6. 

Rigid polyurethane foams have been synthesized from industrial raw materials and phosphorus-containing flame retardants, obtained by the interaction of dialkyl H-phos-phonates with amino alcohols. The phosphorus-containing compounds 1 and 2 are used as modifiers [105]. During polyurethane synthesis, both modifiers speed up the times for foaming, gel formation, and surface drying, and decrease the time for foam growth. 

Work at North Carolina State University has shown that an inclusion compound melt processed into PET film provides substantial flame retardancy. The compound was formed between beta-cyclodextrin and the phosphorus-based flame retardant Antiblaze RD-1. The properties were much better than films containing the separate constituents on their own. 

Several approaches have been used to make polymers fire-retardant. Phosphorus-based flame retardants have been effectively used in a wide variety of polymeric materials. The efficiency of phosphorus compounds is often dramatically increased in the presence of certain nitrogen compounds. Thus, the improved flame resistance of polyesters in the presence of triphenylphosphine oxide and Nylon-6 has been attributed to the synergistic effect of phosphorus and nitrogen atoms. However, the fire-retardant additives (1) frequently influence the decomposition reaction in... 

Inorganic phosphorus compounds are described in the section, commercial Phosphorus-Based Flame Retardants. 

Phosphorus-containing flame retardants may be divided according to the oxidation state of the element into phosphates ((RO)3PO), phosphites ((RO)3P), phos-phonites ((RO)2PR ), phosphinates ((RO)R2PO), phosphine oxides (R3PO), phosphines (R3P), and phosphonium salts (Rj PX). It seems that compounds in which phosphorus has the oxidation states -3, -1, and 1 are the most efficient [6]. These flame retardants function in the solid phase as well as in the gaseous phase. 

Protective Coatings. Some flame retardants function by forming a protective Hquid or char barrier. These minimize transpiration of polymer degradation products to the flame front and/or act as an insulating layer to reduce the heat transfer from the flame to the polymer. Phosphoms compounds that decompose to give phosphoric acid and intumescent systems are examples of this category (see Flame retardants, phosphorus flame retardants). 

One of the principal classes of flame retardants used in plastics and textiles is that of phosphorus, phosphorus—nitrogen, and phosphorus—halogen compounds (see also Flame retardants for textiles). Detailed reviews of phosphoms flame retardants have been pubhshed (1—6) (see also Phosphorus compounds). 

Organophosphorus Derivatives. Neopentyl glycol treated with pyridine and phosphorus trichloride in anhydrous dioxane yields the cycHc hydrogen phosphite, 5,5-dimethyl-l,3-dioxaphosphorinane 2-oxide (2) (32,33). Compounds of this type maybe useful as flameproofing plasticizers, stabilizers, synthetic lubricants, oil additives, pesticides, or intermediates for the preparation of other organophosphoms compounds (see Flame retardants Phosphorus compounds). 

About 80-90% of the elemental P produced is reoxidized to (pure) phosphoric acid (p. 521). The rest is used to make phosphorus oxides (p. 503). sulfides (p. 506), phosphorus chlorides and oxochloride (p. 4%). and organic P compounds. A small amount is convened to red phos rftorus (see below) for use in the striking surface of matches for pyrotechnics and as a flame retarding agent (in polyamides). Bulk price for P4 is S2.00/kg. 

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